1. Field of the Invention
The present invention relates to developing devices, image forming apparatuses, and image forming systems.
2. Description of the Related Art
(1) As one type of image forming apparatus, there is known an apparatus comprising, for example, a rotary-type developing device. The rotary-type developing device comprises a plurality of developing units, which serve as an example of a developer container for developing a latent image formed on a photoconductor using toner, and these developing units are arranged radially about the axis of rotation of the developing device. When an image signal is transmitted from an external device such as a host computer, the image forming apparatus rotates the developing units about the axis of rotation to thereby locate one of the developing units in a developing position opposing the photoconductor. A toner image is formed by developing the latent image formed on the photoconductor, and the image is transferred to an intermediate medium. The image forming apparatus sequentially changes the developing units and repeats the developing and transferring in a similar manner to superimpose a plurality of toner images and thereby form a color image.
There are cases in which the above-described image forming apparatus is used for continuously forming images on a plurality of number of sheets of media using toner of a single color (for example, monochrome). In this continuous image-forming process according to the monochrome image-forming mode, development is carried out using the same developing unit for a long time. Therefore, the developing units will not be subjected to rotation for a long time, in contrast to the case in which color images are formed.
In such a situation, the toner contained in the developing units settles out in the direction of gravity. The settlement of toner causes deterioration in toner flowability. This deterioration in toner flowability causes various problems. For example, the deterioration in toner flowability gives rise to insufficient charging of toner, and as a consequence, it causes a problem that desired images cannot be obtained.
A countermeasure has been proposed in order to avoid such problems. (See, for example, Japanese Patent Application Laid-open Publication No. 2000-347499.) In this method, when images are to be continuously formed on a plurality of number of sheets of media using toner of a single color (for example, monochrome), the developing units are rotated during the continuous image-formation every time the number of sheets of media on which images are formed reaches, for example, a predetermined number of sheets, in order to enhance the flowability of toner.
By adopting the above-described method for enhancing the toner flowability, it is possible to obtain a desired effect if the number of sheets of media on which images are continuously formed is larger than the above-mentioned predetermined number of sheets. If, however, the number of sheets of media on which images are continuously formed is smaller than the predetermined number of sheets, then the following problem arises. An example of such problem is described below.
For example, suppose that the predetermined number of sheets is 48 sheets. When images are continuously formed on 100 sheets of media, then the developing units will be rotated twice during the continuous image-forming process, and thus, the toner flowability will be enhanced. If, however, images are continuously formed on only 40 sheets of media, then the developing units will not be rotated during the continuous image-forming process. Therefore, if the operation of continuously forming images on 40 sheets of media is repeated for several times, then the toner flowability will deteriorate. There will be a more significant deterioration in toner flowability particularly when the number of sheets of media on which images are continuously formed is close to the predetermined number of sheets.
Therefore, there is a need for another method for avoiding the problems caused by deterioration in toner flowability.
(2) As another type of image forming apparatus, there is known an apparatus comprising, for example, a rotary-type developing device. The rotary-type developing device comprises a plurality of developing units, which serve as an example of a developer container for developing a latent image formed on a photoconductor using toner, which serves as an example of developer, and these developing units are arranged radially about the axis of rotation of the developing device. When an image signal is transmitted from an external device such as a host computer, the image forming apparatus rotates the developing units about the axis of rotation to thereby locate one of the developing units in a developing position opposing the photoconductor. A toner image is formed by developing the latent image formed on the photoconductor using the toner bore by a developing roller, which serves as an example of a developer bearing body, and the image is transferred to an intermediate medium. The image forming apparatus sequentially changes the developing units and repeats the developing and transferring in a similar manner to superimpose a plurality of toner images and thereby form a color image.
There are cases in which the above-described image forming apparatus is used for continuously forming images on a plurality of number of sheets of media using toner of a single color (for example, monochrome). In this continuous image-forming process according to the monochrome image-forming mode, development is carried out using the same developing unit for a long time. Therefore, the developing units will not be subjected to rotation for a long time, in contrast to the case in which color images are formed.
If the latent image, which is formed on the photoconductor, is continuously developed using the toner bore by the developing roller in the above-described state in which a developing unit is not rotated for a long time, then the amount of electrical charge of the toner, out of all the toner contained in the developing unit, that is near the developing roller increases excessively. This increase in the amount of electrical charge of toner causes, for example, agglomeration of toner, which gives rise to problems such as image fogging, toner scattering, and toner spilling. Forming images with toner that is in such an inappropriate state will ultimately result in causing a problem that desired images cannot be obtained.
A countermeasure has been proposed in order to avoid such problems. (See, for example, Japanese Patent Application Laid-open Publication No. 2000-347499.) In this method, when images are to be continuously formed on a plurality of number of sheets of media using toner of a single color, the developing units are rotated at a predetermined frequency.
However, since it is not possible to carry out development while the developing units are rotating, there is a disadvantage that the amount of time required for forming images becomes long when the above-described method is employed.
(3) As another type of image forming apparatus, there is known an apparatus comprising, for example, a movable moving member. The movable moving member comprises developing units, which serve as an example of a developer container for developing a latent image formed on a photoconductor using developer. When an image signal is transmitted from an external device such as a host computer, the image forming apparatus moves the developing units to thereby locate the developing units at a developing position opposing the photoconductor. A developer image is formed by developing the latent image formed on the photoconductor, and the image is temporarily transferred to an intermediate medium. The developer image formed on the intermediate transferring body is then transferred onto a medium to form an image thereon. Further, the developing units are configured so that they can be attached to and detached from the moving body. Upon detachment of a developing unit, the moving body moves to a predetermined detachment position, enabling the operator to detach the developing unit. (See, for example, Japanese Patent Application Laid-open Publication No. 11-125969.).
There are cases in which the developer, which is contained in each developing unit described above, spills out from the developing unit and the developer that has spilled adheres to the developing unit. If the operator detaches the developing unit with the developer adhering to it, then the developer on the developing unit may get on the hands of the operator and contaminate his/her hands, or the developer on the developing unit may spill and contaminate the operator or the places around him/her.
(4) As another type of image forming apparatus, there is known an apparatus comprising, for example, an image bearing body for bearing a latent image, and a developing device for developing the latent image bore on the image bearing body with developer. When an image signal is transmitted from an external device such as a host computer, the image forming apparatus moves the developing device to thereby locate the developing device at a developing position opposing the image bearing body. A developer image is formed by developing the latent image formed on the image bearing body, and the image is temporarily transferred to an intermediate medium. The developer image formed on the intermediate transferring body is then transferred onto a medium to form an image thereon. Further, the developing device includes a developer bearing body for bearing the developer, an abutting member that abuts against the developer bearing body, an opposing member that is arranged in opposition to the abutting member on the side opposite from the developer bearing body with respect to the abutting member, and a sealing member for preventing the developer from spilling from between the abutting member and the opposing member. (See, for example, Japanese Patent Application Laid-open Publication No. 9-48458.)
In the above-mentioned case, the sealing member described above is arranged bonded to one of either the abutting member or the opposing member, for example. In such a case, it is necessary to provide the sealing member in the developing device in such a state that the sealing member is highly compressed by the abutting member and the opposing member in order to appropriately prevent the developer from spilling from between the abutting member and the opposing member (particularly from between the sealing member and the member to which the sealing member is not bonded).
In such a situation, the abutting member receives a great force from the compressed sealing member. Therefore, a problem that the functions to be achieved by the abutting member abutting against the developer bearing body are not obtained appropriately may arise.
For example, when a thickness restricting member for restricting the thickness of the layer of the developer bore by the developer bearing body serves as the abutting member, there is a possibility that an excessive restriction load is applied on the thickness restricting member and that it will become difficult to restrict the layer thickness of the developer appropriately. Further, when a developer collecting member for collecting the developer bore by the developer bearing body into the developing device serves as the abutting member, there is a possibility that it will become difficult to collect the developer into the developing device appropriately.